a Department of Geology and Mineralogy, University of Michoacan, Ciudad Universitaria, 58040, Morelia, Michoacan, Mexico
b Dipartimento di Scienze della Terra, Universita Federico II, Via Mezzocannone 8, 80134, Naples, Italy
The zeolitic minerals have been observed in volcanic sequences of recent geologic age (Pliocene-Miocene) that have been located around the Laguna de Cuitzeo and near Morelia (Capital of the State of Michoacan, Mexico). The zeolites of the Cuitzeo area were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), X-ray fluorescence (XRF), FTIR and Raman spectroscopy in combination with thermoanalytical methods (thermogravimetric analysis - TG/DTG - and differential thermal analysis - DTA). The main mineral constituent is an intermediate type of the isomorfous series heulandite-clinoptilolite end members. Trace of feldspars, biotite, and smectite (and an amorphous fraction) were also detected. Chemical composition (Ca 1.44-2.00 K 1.44-0.74 Na 0.05-0.53 Mg 0.67-0.92 Fe 0.02-0.10)[Si 29.04-29.85 Al 6.31-7.04O 72] 13.5 H 2O and some chemical features (Γ=0.96-1.08), (Si/Al ratio 4.47; Al+Fe 3+ of 6.36 to 7.13) with 2.38 (Mg+Ca)>1.43 (Na+K) correspond to the intermediate member of the clinoptilolite-heulandite isomorphous series. The dehydration rate of the Cuitzeo zeolites, especially in the range from 150 to 400°C, as well as spectroscopic features (FTIR and Raman), external cation exchange capacity (135meqkg -1) and porosimetric data are also characteristic for this intermediate clinoptilolite-heulandite member. The value of the BET specific surface area (20.3m 2/g) is about 1.5 times higher than that relative to clinoptilolite-rich tuff powders of different geographic origin and previously characterized. Cuitzeo zeolite deposit is of a great economic interest, considering that it is the unique and richest among the zeolite formations in Southwestern Mexico with zeolite content higher than 70wt.%. This value is relatively high: most of the exploited zeolitic tuffs from the Oaxaca State (the most studied and well known deposits of natural zeolites in the south of Mexico) have been estimated to contain less than 60wt.% zeolite minerals. Based on the above properties the zeolite from Cuitzeo area could be a very effective tool for technological application (such as agricultural use, decontamination of water and soils, cement industry, etc.), particularly due so far of the complete absence of zeolitic deposits in the central region of Mexico.